Semiconductor laser device and method for fabricating the same

ABSTRACT

A first semiconductor laminated structure including a first active layer for oscillating a first laser beam having a first wavelength band is provided on a front-side region of a substrate. A second semiconductor laminated structure including a second active layer for oscillating a second laser beam having a second wavelength band is provided on a rear-side region of the substrate. An emission direction of the first laser beam and an emission direction of the second laser beam are same.

BACKGROUND OF THE INVENTION

The present invention relates to a semiconductor laser device capable ofemitting a plurality of laser beams of different wavelengths, and amethod for fabricating the same.

In recent years, there is an increasing demand for semiconductor laserdevices in many industrial fields, and active researches and developmenthave been performed primarily for semiconductor laser devices includinga group III-V compound semiconductor layer, particularly a compoundsemiconductor layer containing GaAs or InP.

In the field of optical information processing, systems have beenrealized in which data is written or read with a semiconductor laserdevice which includes an AlGaAs layer and oscillates an infrared laserbeam having a wavelength in a 780 nm band. Such semiconductor laserdevices have already been widely used in the field of compact disks(CDs), etc.

A recording apparatus for use with a medium such as an magneto-opticaldisk having a greater capacity than that of a CD employs a semiconductorlaser device which includes an AlGaInP layer and oscillates a laser beamin a 680 nm band shorter than a 780 nm band.

Recently, a digital video disk (DVD) system capable of long-timeplayback of high-definition images requires a semiconductor laser devicewhich emits a red laser beam having a wavelength in a 650 nm band. Thus,it has been attempted to improve the recording density of an opticaldisk through the reduction in oscillation wavelength.

Some DVD apparatuses for reading DVD data have compatibility with CDswhich allows for reading data of both DVDs and CDs so that one canutilize conventional CD data as well as DVD data. Therefore, the lightsource of the pickup head device of such a DVD apparatus needs to beprovided with two semiconductor laser devices, including a firstsemiconductor laser device which includes an AlGaAs layer and emits aninfrared laser beam in a 780 nm band, and a second semiconductor laserdevice which includes an AlGaInP layer and emits a red laser beam in a650 nm band.

In such a case, if an optical processing system is provided for each ofthe semiconductor laser devices, it is necessary to provide an opticalsystem for combining the laser beam in a 780 nm band with the laser beamin a 650 nm band, thereby complicating the structure of the pickup headdevice and imposing a limit on the downsizing of the pickup head device.

In view of this, a hybrid type semiconductor laser device in which twosemiconductor laser devices are arranged adjacent to each other, or amonolithic type semiconductor laser device in which two semiconductorlaminated structures are provided in parallel to each other on a singlesubstrate has been proposed in the art (see Japanese Laid-Open PatentPublication No. 11-186651 and Proc. of the 60th Fall Meeting of JSAP,3a-ZC-10).

FIG. 21 illustrates an example of a conventional monolithic typesemiconductor laser device. The semiconductor laser device includes afirst semiconductor laminated structure 2 including an AlGaInP layer anda second semiconductor laminated structure 3 including an AlGaAs layerwhich are provided on a single semiconductor substrate 1, emitting alaser beam in a 650 nm band from a light-emitting spot 4 of the firstsemiconductor laminated structure 2 and emitting a laser beam in a 780nm band from a light-emitting spot 5 of the second semiconductorlaminated structure 3.

With hybrid type or monolithic type semiconductor laser device asdescribed above, it is no longer necessary to provide an optical systemfor combining two laser beams of different wavelengths, thereby allowingfor simplification and downsizing of the pickup head device.

However, in the hybrid type semiconductor laser device, the pitch of thetwo semiconductor laser devices is influenced by the width dimension ofeach semiconductor laser device. As a result, the pitch of thelight-emitting spots is on the order of 100 μm or more.

In the monolithic type semiconductor laser device, it is necessary toprovide two semiconductor laminated structures on a single semiconductorsubstrate. As a result, the pitch of the light-emitting spots is on theorder of 10 nm or more due to the limit of the process for separatingthe two semiconductor laminated structures from each other.

An optical pickup head device needs to have a half mirror for directingan emitted laser beam toward the optical disk, an object lens forfocusing the laser beam having passed through the half mirror into aspot on the optical disk, a photodetector for detecting the laser beamreflected from the optical disk, etc.

However, since the object lens has been downsized along with thedownsizing of the optical pickup head device, the focusingcharacteristic of the object lens varies due to the variation in thelaser beam incident point on the object lens (the position on the objectlens where the laser beam is incident varies because there are twodifferent light-emitting spots). As a result, it is difficult to focusthe laser beam having passed through the object lens into a tiny spot onthe optical disk.

Moreover, when the angle at which the laser beam having passed throughthe object lens is incident upon the optical disk varies, the directionin which the laser beam is reflected from the optical disk also varies,thereby making it necessary to provide two photodetectors.

SUMMARY OF THE INVENTION

In view of the above-mentioned conventional problems, the presentinvention has been devised for the purpose of emitting a plurality oflaser beams of different wavelengths from a single light-emitting spotor two immediately adjacent light-emitting spots, thereby realizingreliable focusing of the plurality of laser beams of differentwavelengths into a tiny spot on the optical disk and detection of theplurality of laser beams of different wavelengths with a singlephotodetector.

In order to achieve the above-described object, a semiconductor laserdevice according to the present invention includes: a firstsemiconductor laminated structure which is provided on a front-sideregion of a substrate and includes a first active layer for oscillatinga first laser beam having a first wavelength band; and a secondsemiconductor laminated structure which is provided on a rear-sideregion of the substrate and includes a second active layer foroscillating a second laser beam having a second wavelength band, whereinan emission direction of the first laser beam and an emission directionof the second laser beam are same.

In the semiconductor laser device according to the present invention,the first semiconductor laminated structure for oscillating the firstlaser beam is provided on the front-side region of the substrate, andthe second semiconductor laminated structure for oscillating the secondlaser beam is provided on the rear-side region of the substrate, whereinthe emission direction of the first laser beam and the emissiondirection of the second laser beam are same. Therefore, the first andsecond laser beams having different wavelengths can be emitted from asingle light-emitting spot or two immediately adjacent light-emittingspots in the front surface of the first semiconductor laminatedstructure which is provided on the front-side region. Thus, it ispossible to realize reliable focusing of a plurality of laser beams ofdifferent wavelengths into a tiny spot on an optical disk and detectionof the plurality of laser beams of different wavelengths with a singlephotodetector.

In the semiconductor laser device according to the present invention, itis preferred that the emission direction of the first laser beam and theemission direction of the second laser beam are collinear with eachother.

In this way, the first and second laser beams having differentwavelengths can be emitted from a single light-emitting spot in thefront surface of the first semiconductor laminated structure.

In the semiconductor laser device according to the present invention, itis preferred that the emission direction of the second laser beam isabove or below the emission direction of the first laser beam.

In this way, the first and second laser beams having differentwavelengths can be emitted from two immediately adjacent light-emittingspots in the front surface of the first semiconductor laminatedstructure. Since the pitch between the first light-emitting spot and thesecond light-emitting spot is not influenced by the width dimension ofthe semiconductor integrated structure, it is possible to reduce thepitch between the light-emitting spots to be 1 pμm or less.

Moreover, the rear surface of the first active layer can be either atransmissive surface or an absorptive surface, thereby increasing thefreedom in selecting the optical design conditions. When the energy gapof the first active layer is greater than the energy gap of the secondactive layer, and the optical axis of the first laser beam and theoptical axis of the second laser beam are aligned with each other, thefront surface of the second active layer, i.e., the rear surface of thefirst active layer, becomes an absorptive surface for the first laserbeam. Normally, the energy gap of a semiconductor layer above or belowthe second active layer is greater than the energy gap of the secondactive layer. Therefore, if the optical axis of the second laser beam isabove or below the optical axis of the first laser beam, the frontsurface of the semiconductor layer above or below the second activelayer, i.e., the rear surface of the first active layer, can be either atransmissive surface or an absorptive surface for the first laser beam.

When the emission direction of the second laser beam is above or belowthe emission direction of the first laser beam, it is preferred that anenergy gap of a semiconductor layer in the second semiconductorlaminated structure which opposes a rear surface of the first activelayer is greater than an energy gap of the first active layer.

In this way, the semiconductor layer in the second semiconductorlaminated structure which opposes the rear surface of the first activelayer transmits the first laser beam therethrough, thereby reducing theloss of the first laser beam.

When the emission direction of the second laser beam is above or belowthe emission direction of the first laser beam, it is preferred that thefirst semiconductor laminated structure includes a first cladding layerlocated between the substrate and the first active layer and a secondcladding layer located above the first active layer; the secondsemiconductor laminated structure includes a third cladding layerlocated between the substrate and the second active layer and a fourthcladding layer located above the second active layer; and a compositionof the first cladding layer and a composition of the third claddinglayer are same, or a composition of the second cladding layer and acomposition of the fourth cladding layer are same.

In the semiconductor laser device according to the present invention, itis preferred that an energy gap of the first active layer is greaterthan an energy gap of the second active layer.

In this way, the second laser beam is not absorbed while it propagatesthrough the first semiconductor laminated structure, and thus isreliably emitted from the front surface of the first semiconductorlaminated structure.

Especially when the optical axis of the first laser beam and the opticalaxis of the second laser beam are aligned with each other, since thesecond active layer has a large absorption coefficient for the firstlaser beam oscillated in the first active layer, the first laser beam isoscillated with the front surface of the first semiconductor laminatedstructure and the front surface of the second semiconductor laminatedstructure serving as resonator surfaces. Moreover, since the firstactive layer is transparent to the second laser beam oscillated in thesecond active layer, the second laser beam is oscillated with the frontsurface of the first semiconductor laminated structure and the rearsurface of the second semiconductor laminated structure serving asresonator surfaces. Therefore, two laser beams of different wavelengthbands can be reliably emitted from a single light-emitting spot.

In the semiconductor laser device according to the present invention, itis preferred that the first active layer contains indium and phosphorus;and the second active layer contains gallium and arsenic.

In this way, the first laser beam has an oscillation wavelength of about650 nm and is a red laser beam, and the second laser beam has anoscillation wavelength of about 780 nm and is an infrared laser beam.Thus, it is possible to obtain a semiconductor laser device which isoptimal for use in a pickup head device of a DVD apparatus.

In the semiconductor laser device according to the present invention, itis preferred that a front surface of the first semiconductor laminatedstructure is coated with a non-reflection coating layer; and a rearsurface of the second semiconductor laminated structure is coated with ahigh-reflection coating layer.

In this way, two laser beams of different wavelength bands can bereliably emitted from the front surface of the first semiconductorlaminated structure.

In the semiconductor laser device according to the present invention, itis preferred that the semiconductor laser device further includes adielectric member between a rear surface of the first semiconductorlaminated structure and a front surface of the second semiconductorlaminated structure; and the dielectric member has a refractive indexwhich is between an effective refractive index of a stripe region of thefirst active layer and an effective refractive index of a stripe regionof the second active layer.

In this way, the insulation between the first semiconductor laminatedstructure and the second semiconductor laminated structure can beensured by the dielectric member. Moreover, the optical couplingefficiency between the first laser beam and the second semiconductorlaminated structure is improved, and the optical coupling efficiencybetween the second laser beam and the first semiconductor laminatedstructure is also improved, thereby improving the opticalcharacteristics of the semiconductor laser device.

A first method for fabricating a semiconductor laser device according tothe present invention is a method for fabricating a semiconductor laserdevice including: a first semiconductor laminated structure which isprovided on a front-side region of a substrate and includes a firstactive layer for oscillating a first laser beam having a firstwavelength band; and a second semiconductor laminated structure which isprovided on a rear-side region of the substrate and includes a secondactive layer for oscillating a second laser beam having a secondwavelength band, the method including the steps of: growing a firsttentative semiconductor laminated structure having the same laminatedstructure as the second semiconductor laminated structure on thesubstrate; removing a front-side portion of the first tentativesemiconductor laminated structure, thereby producing the secondsemiconductor laminated structure on the rear-side region of thesubstrate; growing a second tentative semiconductor laminated structurehaving the same laminated structure as the first semiconductor laminatedstructure on the front-side region of the substrate and on the secondsemiconductor laminated structure; and removing a portion of the secondtentative semiconductor laminated structure above the secondsemiconductor laminated structure, thereby producing the firstsemiconductor laminated structure on the front-side region of thesubstrate.

With the first method for fabricating a semiconductor laser deviceaccording to the present invention, it is possible to reliably fabricatea monolithic type semiconductor laser device, wherein the firstsemiconductor laminated structure for oscillating the first laser beamis provided on the front-side region of the substrate, and the secondsemiconductor laminated structure for oscillating the second laser beamis provided on the rear-side region of the substrate, and wherein theemission direction of the first laser beam and the emission direction ofthe second laser beam are same.

A second method for fabricating a semiconductor laser device accordingto the present invention is a method for fabricating a semiconductorlaser device including: a first semiconductor laminated structure whichis provided on a front-side region of a substrate and includes a firstactive layer for oscillating a first laser beam having a firstwavelength band; and a second semiconductor laminated structure which isprovided on a rear-side region of the substrate and includes a secondactive layer for oscillating a second laser beam having a secondwavelength band, the method including the steps of: growing a firsttentative semiconductor laminated structure having the same laminatedstructure as the first semiconductor laminated structure on thesubstrate; removing a rear-side portion of the first tentativesemiconductor laminated structure, thereby producing the firstsemiconductor laminated structure on the front-side region of thesubstrate; growing a second tentative semiconductor laminated structurehaving the same laminated structure as the second semiconductorlaminated structure on the rear-side region of the substrate and on thefirst semiconductor laminated structure; and removing a portion of thesecond tentative semiconductor laminated structure above the firstsemiconductor laminated structure, thereby producing the secondsemiconductor laminated structure on the rear-side region of thesubstrate.

With the second method for fabricating a semiconductor laser deviceaccording to the present invention, it is possible to reliably fabricatea monolithic type semiconductor laser device, wherein the firstsemiconductor laminated structure for oscillating the first laser beamis provided on the front-side region of the substrate, and the secondsemiconductor laminated structure for oscillating the second laser beamis provided on the rear-side region of the substrate, and wherein theemission direction of the first laser beam and the emission direction ofthe second laser beam are same.

A third method for fabricating a semiconductor laser device according tothe present invention includes: a first step of providing a first laserchip including a first active layer for oscillating a first laser beamhaving a first wavelength band and a second laser chip including asecond active layer for oscillating a second laser beam having a secondwavelength band; and a second step of fixing the first laser chip to afront-side region of a substrate and fixing the second laser chip to arear-side region of the substrate, wherein the second step includes thestep of fixing the first laser chip and the second laser chip so that anemission direction of the first laser beam and an emission direction ofthe second laser beam are same.

With the third method for fabricating a semiconductor laser deviceaccording to the present invention, it is possible to reliably fabricatea hybrid type semiconductor laser device, wherein the first laser chipfor oscillating the first laser beam is provided on the front-sideregion of the substrate, and the second laser chip for oscillating thesecond laser beam is provided on the rear-side region of the substrate,and wherein the emission direction of the first laser beam and theemission direction of the second laser beam are same.

In the first to third methods for fabricating a semiconductor laserdevice, it is preferred that the emission direction of the first laserbeam and the emission direction of the second laser beam are collinearwith each other.

In this way, the first and second laser beams of different wavelengthscan be emitted from a single light-emitting spot in the front surface ofthe first semiconductor laminated structure or the first laser chip.

In the first to third methods for fabricating a semiconductor laserdevice, it is preferred that the emission direction of the second laserbeam is above or below the emission direction of the first laser beam.

In this way, the first and second laser beams having differentwavelengths can be emitted from two immediately adjacent light-emittingspots in the front surface of the first semiconductor laminatedstructure. Since the pitch between the first light-emitting spot and thesecond light-emitting spot is not influenced by the width dimension ofthe semiconductor integrated structure, it is possible to reduce thepitch between the light-emitting spots to be 1 μm or less.

In the first to third methods for fabricating a semiconductor laserdevice, it is preferred that an energy gap of the first active layer isgreater than an energy gap of the second active layer.

In this way, the second laser beam is not absorbed while it propagatesthrough the first laser chip, and thus is reliably emitted from thefront surface of the first semiconductor laminated structure or thefirst laser chip.

Especially when the optical axis of the first laser beam and the opticalaxis of the second laser beam are aligned with each other, since thesecond active layer has a large absorption coefficient for the firstlaser beam oscillated in the first active layer, the first laser beam isoscillated with the front surface of the first semiconductor laminatedstructure or the first laser chip and the front surface of the secondsemiconductor laminated structure or the second laser chip serving asresonator surfaces. Moreover, since the first active layer istransparent to the second laser beam oscillated in the second activelayer, the second laser beam is oscillated with the front surface of thefirst semiconductor laminated structure or the first laser chip and therear surface of the second semiconductor laminated structure or thesecond laser chip serving as resonator surfaces. Therefore, two laserbeams of different wavelength bands can be reliably emitted from asingle light-emitting spot.

In the first to third methods for fabricating a semiconductor laserdevice, it is preferred that the first active layer contains indium andphosphorus; and the second active layer contains gallium and arsenic.

In this way, the first laser beam has an oscillation wavelength of about650 nm and is a red laser beam, and the second laser beam has anoscillation wavelength of about 780 nm and is an infrared laser beam.Thus, it is possible to obtain a semiconductor laser device which isoptimal for use in a pickup head device of a DVD apparatus.

The first to third methods for fabricating a semiconductor laser devicepreferably further include the steps of: coating a front surface of thefirst semiconductor laminated structure with a non-reflection coatinglayer; and coating a rear surface of the second semiconductor laminatedstructure with a high-reflection coating layer.

In this way, two laser beams of different wavelength bands can bereliably emitted from the front surface of the first semiconductorlaminated structure or the first laser chip.

The third method for fabricating a semiconductor laser device preferablyfurther includes, after the second step, the step of filling a gapbetween a rear surface of the first laser chip and a front surface ofthe second laser chip with a dielectric member having a refractive indexwhich is between an effective refractive index of a stripe region of thefirst active layer and an effective refractive index of a stripe regionof the second active layer.

In this way, the insulation between the first laser chip and the secondlaser chip can be ensured by the dielectric member. Moreover, theoptical coupling efficiency between the first laser beam and the secondlaser chip is improved, and the optical coupling efficiency between thesecond laser beam and the first laser chip is also improved, therebyimproving the optical characteristics of the semiconductor laser device.

A fourth method for fabricating a semiconductor laser device accordingto the present invention includes: a first step of providing a firstlaser chip including a first active layer for oscillating a first laserbeam having a first wavelength band, a second laser chip including asecond active layer for oscillating a second laser beam having a secondwavelength band, and a third laser chip including a third active layerfor oscillating a third laser beam having a third wavelength band; and asecond step of fixing the first laser chip to a front-side region of asubstrate, fixing the second laser chip to a central region of thesubstrate, and fixing the third laser chip to a rear-side region of thesubstrate, wherein the second step includes the step of fixing the firstlaser chip, the second laser chip and the third laser chip so that anemission direction of the first laser beam, an emission direction of thesecond laser beam, and an emission direction of the third laser beam aresame.

With the fourth method for fabricating a semiconductor laser deviceaccording to the present invention, it is possible to reliably fabricatea hybrid type semiconductor laser device, wherein the first laser chipfor oscillating the first laser beam is provided on the front-sideregion of the substrate, the second laser chip for oscillating thesecond laser beam is provided in the central region of the substrate,and the third laser chip for oscillating the third laser beam isprovided on the rear-side region of the substrate, and wherein theemission direction of the first laser beam, the emission direction ofthe second laser beam and the emission direction of the-third laser beamare same.

In the fourth method for fabricating a semiconductor laser device, it ispreferred that the emission direction of the third laser beam iscollinear with the emission direction of the first laser beam or theemission direction of the second laser beam.

In this way, the third laser beam and the first or second laser beamhaving different wavelengths can be reliably emitted from a singlelight-emitting spot in the front surface of the first laser chip.

In the fourth method for fabricating a semiconductor laser device, it ispreferred that an energy gap of the first active layer is greater thanan energy gap of the second active layer; and the energy gap of thesecond active layer is greater than an energy gap of the third activelayer.

In this way, the second laser beam is not absorbed while it propagatesthrough the first laser chip, and the third laser beam is not absorbedwhile it propagates through the first and second laser chips. Thus, thesecond and third laser beams are reliably emitted from the front surfaceof the first laser chip.

In the fourth method for fabricating a semiconductor laser device, it ispreferred that the first active layer contains gallium and nitrogen; thesecond active layer contains indium and phosphorus; and the third activelayer contains gallium and arsenic.

In this way, the first laser beam is a blue laser beam, the second laserbeam is a red laser beam, and the third laser beam is an infrared laserbeam. Thus, three laser beams of different oscillation wavelengths canbe emitted from a single light-emitting spot or two immediately adjacentlight-emitting spots. As a result, it is possible to realize athree-wavelength semiconductor laser device capable of accommodatingthree types of optical disks of different standards.

The fourth method for fabricating a semiconductor laser devicepreferably further includes, after the second step, the steps of:filling a gap between a rear surface of the first laser chip and a frontsurface of the second laser chip with a first dielectric member having arefractive index which is between an effective refractive index of astripe region of the first active layer and an effective refractiveindex of a stripe region of the second active layer; and filling a gapbetween a rear surface of the second laser chip and a front surface ofthe third laser chip with a second dielectric member having a refractiveindex which is between the effective refractive index of the striperegion of the second active layer and an effective refractive index of astripe region of the third active layer.

In this way, the insulation between the first laser chip and the secondlaser chip and the insulation between the second laser chip and thethird laser chip can be ensured. Moreover, the optical couplingefficiency between each laser beam and each laser chip is improved,thereby improving the optical characteristics of the semiconductor laserdevice. BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view illustrating a semiconductor laser deviceaccording to Embodiment 1.

FIG. 2 is a cross-sectional view illustrating the semiconductor laserdevice according to Embodiment 1 taken along line II-II of FIG. 1.

FIG. 3 is a cross-sectional view illustrating a semiconductor laserdevice according to Embodiment 2.

FIG. 4 is a perspective view illustrating a semiconductor laser deviceaccording to Embodiment 3.

FIG. 5 is a cross-sectional view illustrating the semiconductor laserdevice according to Embodiment 3 taken along line V-V of FIG. 4.

FIG. 6A and FIG. 6B illustrate one step in a method for fabricating thesemiconductor laser device according to Embodiment 3, wherein FIG. 6A isa perspective view, and FIG. 6B is a cross-sectional view taken alongline VIb-VIb of FIG. 6A.

FIG. 7A and FIG. 7B illustrate one step in the method for fabricatingthe semiconductor laser device according to Embodiment 3, wherein FIG.7A is a perspective view, and FIG. 7B is a cross-sectional view takenalong line VIIb-VIIb of FIG. 7A.

FIG. 8A and FIG. 8B illustrate one step in the method for fabricatingthe semiconductor laser device according to Embodiment 3, wherein FIG.8A is a perspective view, and FIG. 8B is a cross-sectional view takenalong line VIIIb-VIIIb of FIG. 8A.

FIG. 9A and FIG. 9B illustrate one step in the method for fabricatingthe semiconductor laser device according to Embodiment 3, wherein FIG.9A is a perspective view, and FIG. 9B is a cross-sectional view takenalong line IXb-IXb of FIG. 9A.

FIG. 10A and FIG. 10B illustrate one step in the method for fabricatingthe semiconductor laser device according to Embodiment 3, wherein FIG.10A is a perspective view, and FIG. 10B is a cross-sectional view takenalong line Xb-Xb of FIG. 10A.

FIG. 11A and FIG. 11B illustrate one step in the method for fabricatingthe semiconductor laser device according to Embodiment 3, wherein FIG.11A is a perspective view, and FIG. 11B is a cross-sectional view takenalong line XIb-XIb of FIG. 11A.

FIG. 12 is a perspective view illustrating a semiconductor laser deviceaccording to the first variation of Embodiment 3.

FIG. 13 is a cross-sectional view illustrating the semiconductor laserdevice according to the first variation of Embodiment 3 taken along lineXIII-XIII of FIG. 12.

FIG. 14A and FIG. 14B illustrate a semiconductor laser device accordingto the second variation of Embodiment 3, wherein FIG. 14A is aperspective view, and FIG. 14B is a cross-sectional view taken alongline XIVb-XIVb of FIG. 14A.

FIG. 15A and FIG. 15B illustrate a semiconductor laser device accordingto Embodiment 4, wherein FIG. 15A is a perspective view, and FIG. 15B isa cross-sectional view taken along line XVb-XVb of FIG. 15A.

FIG. 16A and FIG. 16B illustrate a semiconductor laser device accordingto Embodiment 5, wherein FIG. 16A is a perspective view, and FIG. 16B isa cross-sectional view taken along line XVIb-XVIb of FIG. 16A.

FIG. 17 is a perspective view illustrating a semiconductor laser deviceaccording to one variation of Embodiment 5.

FIG. 18 is a cross-sectional view illustrating a semiconductor laserdevice according to Embodiment 6.

FIG. 19A to FIG. 19C are perspective views respectively illustratingdifferent steps in a method for fabricating the semiconductor laserdevice according to Embodiment 6.

FIG. 20 is a perspective view illustrating one step in the method forfabricating the semiconductor laser device according to Embodiment 6.

FIG. 21 is a perspective view illustrating an example of a monolithictype semiconductor laser device as a conventional semiconductor laserdevice.

DETAILED DESCRIPTION OF THE INVENTION EMBODIMENT 1

A semiconductor laser device according to Embodiment 1 of the presentinvention and a method for fabricating the same will now be describedwith reference to FIG. 1 and FIG. 2. FIG. 1 is a perspective viewillustrating the semiconductor laser device according to Embodiment 1,and FIG. 2 is a cross-sectional view taken along line II-II of FIG. 1.

As illustrated in FIG. 1 and FIG. 2, a first semiconductor laminatedstructure 110 which includes an AlGaInP layer and has an oscillationwavelength in a 650 nm band is provided on a front-side region of ann-type GaAs substrate 100, and a second semiconductor laminatedstructure 120 which includes an AlGaAs layer and has an oscillationwavelength in a 780 nm band is provided on a rear-side region of then-type GaAs substrate 100.

The first semiconductor laminated structure 110 includes: an n-typecladding layer 111 made of an n-type AlGaInP layer; an active layer 112made of a stack of AlGaInP layers (barrier layers) and GaInP layers(well layers); a p-type first cladding layer 113 made of a p-typeAlGaInP layer; a pair of current blocking layers 114 made of an n-typeAlInP layer; a p-type second cladding layer 115 made of a p-type AlGaInPlayer; and a contact layer 116 made of a p-type GaAs layer. These layersare successively provided in this order from bottom to top on thefront-side region of the n-type GaAs substrate 100 on the upper surfaceof the first semiconductor laminated structure 110, there is provided afirst p-type electrode 117 which is made of a laminated film ofCr/Pt/Au, for example, and is in ohmic contact with the contact layer116. The composition of the mixed crystal of the active layer 112 isselected so that the laser oscillation wavelength thereof is in a 650 nmband.

The second semiconductor laminated structure 120 includes: an n-typecladding layer 121 made of an n-type AlGaAs layer; an active layer 122made of a stack of AlGaAs layers (barrier layers) and. GaAs layers (welllayers); a p-type first cladding layer 123 made of a p-type AlGaAslayer; a pair of current blocking layers 124 made of an n-type AlGaAslayer; a p-type second cladding layer 125 made of a p-type AlGaAs layer;and a contact layer 126 made of a p-type GaAs layer. These layers aresuccessively provided in this order from bottom to top on the rear-sideregion of the n-type GaAs substrate 100. On the upper surface of thesecond semiconductor laminated structure 120, there is provided a secondp-type electrode 127 which is made of a laminated film of Cr/Pt/Au, forexample, and is in ohmic contact with the contact layer 126. Thecomposition of the mixed crystal of the active layer 122 is selected sothat the laser oscillation wavelength thereof is in a 780 nm band.

On the lower surface of the first semiconductor laminated structure 110and the second semiconductor laminated structure 120, there is providedan n-type electrode 133 which contains Au, Ge and Ni, for example, andis in ohmic contact with the n-type GaAs substrate 100.

In an upper portion of the junction between the first semiconductorlaminated structure 110 and the second semiconductor laminated structure120, there is provided a groove portion 134 which extends in a directionperpendicular to the direction of the optical waveguide. The grooveportion 134 electrically insulates the contact layer 116 and the firstp-type electrode 117 of the first semiconductor laminated structure 110from the contact layer 126 and the second p-type electrode 127 of thesecond semiconductor laminated structure 120.

The center line between the pair of current blocking layers 114 in thefirst semiconductor laminated structure 110 and that between the pair ofcurrent blocking layers 124 in the second semiconductor laminatedstructure 120 are aligned with each other, and the thickness of then-type cladding layer 111 of the first semiconductor laminated structure110 and that of the n-type cladding layer 121 of the secondsemiconductor laminated structure 120 are set to be equal to each other.As a result, the center line of a stripe region 112 a of the activelayer 112 of the first semiconductor laminated structure 110 and that ofa stripe region 122 a of the active layer 122 of the secondsemiconductor laminated structure 120 are aligned with each other.

The first semiconductor laminated structure 110 and the secondsemiconductor laminated structure 120 are attached to each other alongan interface 135. A front cleavage plane 131, which is the front surfaceof the first semiconductor laminated structure 110, is coated with anon-reflection coating layer 136 made of a dielectric film such assilicon oxide, silicon nitride or aluminum oxide, whereas a rearcleavage plane 132, which is the rear surface of the secondsemiconductor laminated structure 120, is coated with a high-reflectioncoating layer 137 including a dielectric film such as silicon oxide,silicon nitride or aluminum oxide, and an amorphous silicon film whichare laminated on each other. In FIG. 1, the non-reflection coating layer136 and the high-reflection coating layer 137 are not shown for the sakeof simplicity.

The operation of the semiconductor laser device according to Embodiment1 will now be described.

First, when a current is injected from the first p-type electrode 117,the current is confined into a region between the pair of currentblocking layers 114 in the p-type second cladding layer 115, therebyoscillating a first laser beam having an oscillation wavelength in a 650nm band in the stripe region 112 a of the active layer 112. In thiscase, since the energy gap of an AlGaInP layer is greater than that ofan AlGaAs layer, the active layer 122 including an AlGaAs layer has alarge absorption coefficient for the first laser beam oscillated in theactive layer 112 including an AlGaInP layer. As a result, the firstlaser beam is oscillated in the stripe region 112 a of the active layer112 with the front cleavage plane 131 and the interface 135 serving asresonator surfaces. Thus, the first laser beam having a wavelength in a650 nm band is emitted from the front cleavage plane 131 which is coatedwith the non-reflection coating layer 136.

When a current is injected from the second p-type electrode 127, thecurrent is confined into a region between the pair of current blockinglayers 124 in the p-type second cladding layer 125, thereby oscillatinga second laser beam having an oscillation wavelength in a 780 nm band inthe stripe region 122 a of the active layer 122. In this case, since thecenter line of the stripe region 112 a of the active layer 112 of thefirst semiconductor laminated structure 110 and that of the striperegion 122 a of the active layer 122 of the second semiconductorlaminated structure 120 are aligned with each other, and the activelayer 112 including an AlGaInP layer has a small absorption coefficientfor the second laser beam and is transparent to the second laser beam,the second laser beam is oscillated with the front cleavage plane 131and the rear cleavage plane 132 serving as resonator surfaces. Since therear cleavage plane 132 is coated with the high-reflection coating layer137, the second laser beam having a wavelength in a 780 nm band isemitted from the front cleavage plane 131.

Therefore, two laser beams, the first laser beam and the second laserbeam, having different wavelengths can be emitted from a singlelight-emitting spot in the front cleavage plane 131.

In Embodiment 1, the first semiconductor laminated structure 110includes an AlGaInP layer and the second semiconductor laminatedstructure 120 includes an AlGaAs layer. Alternatively, it is possible toemploy the combination of a first semiconductor laminated structurelocated on the front side and including an AlGaN layer and a secondsemiconductor laminated structure located on the rear side and includingan AlGaInP layer so that a blue-violet laser beam in a 400 nm band and ared laser beam in a 650 nm band are emitted. Alternatively, it ispossible to employ the combination of a first semiconductor laminatedstructure located on the front side and including an AlGaN layer and asecond semiconductor laminated structure located on the rear side andincluding an AlGaAs layer so that a blue-violet laser beam in a 400 nmband and an infrared laser beam in a 780 nm band are emitted. In atwo-wavelength semiconductor laser device, the semiconductor laminatedstructure emitting a laser beam of the shorter wavelength is preferablyarranged on the laser beam emitting side.

A method for fabricating the semiconductor laser device according toEmbodiment 1 will now be described.

A first fabrication method is as follows. The first semiconductorlaminated structure 110 and the second semiconductor laminated structure120 in which the n-type cladding layer 111 and the n-type cladding layer121 have the same thickness are produced separately. The firstsemiconductor laminated structure 110 is attached to a front-side regionof the n-type GaAs substrate 100 by using a solder, or the like, and thesecond semiconductor laminated structure 120 is attached to a rear-sideregion of the n-type GaAs substrate 100 by using a solder, or the like.This is done so that the center line between the pair of currentblocking layers 114 in the first semiconductor laminated structure 110and that between the pair of current blocking layers 124 in the secondsemiconductor laminated structure 120 are aligned with each other. Inthis way, the center line of the stripe region 112 a of the active layer112 of the first semiconductor laminated structure 110 and that of thestripe region 122 a of the active layer 122 of the second semiconductorlaminated structure 120 are aligned with each other. With the firstfabrication method, since neither the first semiconductor laminatedstructure 110 nor the second semiconductor laminated structure 120 needsto be provided through crystal growth, a conductive substrate, e.g., asilicon substrate, may be used instead of the n-type GaAs substrate 100.

A second fabrication method is as follows. The first semiconductorlaminated structure 110 is provided on the n-type GaAs substrate 100,with the second semiconductor laminated structure 120 being providedseparately. After a rear-side region of the first semiconductorlaminated structure 110 is removed by etching, the second semiconductorlaminated structure 120 is attached to the rear-side region.Alternatively, the second semiconductor laminated structure 120 isprovided on the n-type GaAs substrate 100, with the first semiconductorlaminated structure 110 being provided separately. After a front-sideregion of the second semiconductor laminated structure 120 is removed byetching, the first semiconductor laminated structure 110 is attached tothe front-side region.

EMBODIMENT 2

A semiconductor laser device according to Embodiment 2 of the presentinvention will now be described with reference to FIG. 3.

As illustrated in FIG. 3, a first semiconductor laminated structure 210which includes an AlGaN layer and has an oscillation wavelength in a 400nm band is provided on a front-side region of an n-type GaAs substrate200, a second semiconductor laminated structure 220 which includes anAlGaInP layer and has an oscillation wavelength in a 650 nm band isprovided in a central region of the n-type GaAs substrate 200, and athird semiconductor laminated structure 230 which includes an AlGaAslayer and has an oscillation wavelength in a 780 nm band is provided ona rear-side region of the n-type GaAs substrate 200. In FIG. 3, a p-typeelectrode, a contact layer and an n-type electrode are not shown.

The first semiconductor laminated structure 210 has an active layer 211whose mixed crystal composition is selected so that the laseroscillation wavelength thereof is in a 400 nm band. The secondsemiconductor laminated structure 220 includes an active layer 221 whosemixed crystal composition is selected so that the laser oscillationwavelength thereof is in a 650 nm band. The third semiconductorlaminated structure 230 includes an active layer 231 whose mixed crystalcomposition is selected so that the laser oscillation wavelength thereofis in a 780 nm band.

A front cleavage plane 241 of the first semiconductor laminatedstructure 210 is coated with a non-reflection coating layer 243, and arear cleavage plane 242 of the third semiconductor laminated structure230 is coated with a high-reflection coating layer 244.

In Embodiment 2, the energy gap of the active layer increases throughthe first semiconductor laminated structure 210, the secondsemiconductor laminated structure 220 and the third semiconductorlaminated structure 230 in this order, i.e., successively from the frontside. Therefore, in the active layer 211 of the first semiconductorlaminated structure 210, a blue-violet laser beam having a wavelength ina 400 nm band is oscillated with the front cleavage plane 241 and afirst interface 245 serving as resonator surfaces. In the active layer221 of the second semiconductor laminated structure 220, a red laserbeam having a wavelength in a 650 nm band is oscillated with the frontcleavage plane 241 and a second interface 246 serving as resonatorsurfaces. In the active layer 231 of the third semiconductor laminatedstructure 230, an infrared laser beam having a wavelength in a 780 nmband is oscillated with the front cleavage plane 241 and the rearcleavage plane 242 serving as resonator surfaces. Moreover, the frontcleavage plane 241 is coated with the non-reflection coating layer 243,and the rear cleavage plane 242 is coated with the high-reflectioncoating layer 244. As a result, a blue-violet laser beam having awavelength in a 400 nm band, a red laser beam having a wavelength in a650 nm band and an infrared laser beam having a wavelength in a 780 nmband are emitted from the front cleavage plane 241.

EMBODIMENT 3

A semiconductor laser device according to Embodiment 3 of the presentinvention will now be described with reference to FIG. 4 and FIG. 5.FIG. 4 is a perspective view illustrating the semiconductor laser deviceaccording to Embodiment 3, and FIG. 5 is a cross-sectional view takenalong line V-V of FIG. 4.

As illustrated in FIG. 4 and FIG. 5, a first semiconductor laminatedstructure 310 which includes an AlGaInP layer and has an oscillationwavelength in a 650 nm band is provided on a front-side region of ann-type GaAs substrate 300, and a second semiconductor laminatedstructure 320 which includes an AlGaAs layer and has an oscillationwavelength in a 780 nm band is provided on a rear-side region of then-type GaAs substrate 300. A side-wall growth portion 338 made of alaminated structure including an AlGaInP layer is provided at a rear endof the first semiconductor laminated structure 310.

The first semiconductor laminated structure 310 includes: an n-typecladding layer 311 made of an n-type AlGaInP layer; an active layer 312made of a stack of AlGaInP layers (barrier layers) and GaInP layers(well layers); a p-type first cladding layer 313 made of a p-typeAlGaInP layer; a pair of current blocking layers 314 made of an n-typeAlInP layer; a p-type second cladding layer 315 made of a p-type AlGaInPlayer; and a contact layer 316 made of a p-type GaAs layer. These layersare successively provided in this order from bottom to top on thefront-side region of the n-type GaAs substrate 300. On the upper surfaceof the first semiconductor laminated structure 310, there is provided afirst p-type electrode 317 which is in ohmic contact with the contactlayer 316. The composition of the mixed crystal of the active layer 312is selected so that the laser oscillation wavelength thereof is in a 650nm band.

The second semiconductor laminated structure 320 includes: an n-typecladding layer 321 made of an n-type AlGaAs layer; an active layer 322made of a stack of AlGaAs layers (barrier layers) and GaAs layers (welllayers); a p-type first cladding layer 323 made of a p-type AlGaAslayer; a pair of current blocking layers 324 made of an n-type AlGaAslayer; a p-type second cladding layer 325 made of a p-type AlGaAs layer;and a contact layer 326 made of a p-type GaAs layer. These layers aresuccessively provided in this order from bottom to top on the rear-sideregion of the n-type GaAs substrate 300. On the upper surface of thesecond semiconductor laminated structure 320, there is provided a secondp-type electrode 327 which is in ohmic contact with the contact layer326. The composition of the mixed crystal of the active layer 322 isselected so that the laser oscillation wavelength thereof is in a 780 nmband.

On the bottom surface of the first semiconductor laminated structure 310and the second semiconductor laminated structure 320, there is providedan n-type electrode 333 which is in ohmic contact with the n-type GaAssubstrate 300.

The first semiconductor laminated structure 310 and the secondsemiconductor laminated structure 320 are attached to each other alongan interface 335. In an upper portion of the junction between the firstsemiconductor laminated structure 310 and the second semiconductorlaminated structure 320, there is provided a groove portion 334 whichextends in a direction perpendicular to the direction of the opticalwaveguide. The groove portion 334 electrically insulates the contactlayer 316 and the first p-type electrode 317 of the first semiconductorlaminated structure 310 from the contact layer 326 and the second p-typeelectrode 327 of the second semiconductor laminated structure 320. Theside-wall growth portion 338 protrudes above the bottom surface of thegroove portion 334.

A front cleavage plane 331 of the first semiconductor laminatedstructure 310 is coated with a non-reflection coating layer 336, and arear cleavage plane 332 of the second semiconductor laminated structure320 is coated with a high-reflection coating layer 337.

The center line between the pair of current blocking layers 314 in thefirst semiconductor laminated structure 310 and that between the pair ofcurrent blocking layers 324 in the second semiconductor laminatedstructure 320 are aligned with each other, and the thickness of then-type cladding layer 311 of the first semiconductor laminated structure310 and that of the n-type cladding layer 321 of the secondsemiconductor laminated structure 320 are set to be equal to each other.As a result, the center line of a stripe region 312 a of the activelayer 312 of the first semiconductor laminated structure 310 and that ofa stripe region 322 a of the active layer 322 of the secondsemiconductor laminated structure 320 are aligned with each other.

The operation of the semiconductor laser device according to Embodiment3 will now be described.

First, when a current is injected from the first p-type electrode 317,the current is confined into a region between the pair of currentblocking layers 314 in the p-type second cladding layer 315, therebyoscillating a first laser beam having an oscillation wavelength in a 650nm band in the stripe region 312 a of the active layer 312. In this;case, while the first laser beam is oscillated in the stripe region 312a of the active layer 312 with the front cleavage plane 331 and theinterface 335 serving as resonator surfaces, the influence of theside-wall growth portion 338 can be ignored because the width dimensionof the side-wall growth portion 338 is very small with respect to theresonator length. Therefore, the first laser beam having a wavelength ina 650 nm band is emitted from the front cleavage plane 331 which iscoated with the non-reflection coating layer 336.

When a current is injected from the second p-type electrode 327, thecurrent is confined into a region between the pair of current blockinglayers 324 in the p-type second cladding layer 325, thereby oscillatinga second laser beam having an oscillation wavelength in a 780 nm band inthe stripe region 322 a of the active layer 322. Since the center lineof the stripe region 312 a of the active layer 312 of the firstsemiconductor laminated structure 310 and that of the stripe region 322a of the active layer 322 of the second semiconductor laminatedstructure 320 are aligned with each other, and the active layer 312including an AlGaInP layer has a small absorption coefficient for thesecond laser beam and is transparent to the second laser beam, thesecond laser beam is oscillated with the front cleavage plane 331 andthe rear cleavage plane 332 serving as resonator surfaces. Since therear cleavage plane 332 is coated with the high-reflection coating layer337, the-second laser beam having a wavelength in a 780 nm band isemitted from the front cleavage plane 331.

Therefore, two laser beams, the first laser beam and the second laserbeam, having different wavelengths can be emitted from a singlelight-emitting spot in the front cleavage plane 331.

In Embodiment 3, the first semiconductor laminated structure 310includes an AlGaInP layer and the second semiconductor laminatedstructure 320 includes an AlGaAs layer. Alternatively, it is possible toemploy the combination of a first semiconductor laminated structurelocated on the front side and including an AlGaN layer and a secondsemiconductor laminated structure located on the rear side and includingan AlGaInP layer so that a blue-violet laser beam in a 400 nm band and ared laser beam in a 650 nm band are emitted. Alternatively, it ispossible to employ the combination of a first semiconductor laminatedstructure located on the front side and including an AlGaN layer and asecond semiconductor laminated structure located on the rear side andincluding an AlGaAs layer so that a blue-violet laser beam in a 400 nmband and an infrared laser beam in a 780 nm band are emitted. In atwo-wavelength semiconductor laser device, the semiconductor laminatedstructure emitting a laser beam of the shorter wavelength is preferablyarranged on the laser beam emitting side.

A method for fabricating the semiconductor laser device according toEmbodiment 3 will now be described with reference to FIG. 6A, FIG., 6B,FIG. 7A, FIG. 7B, FIG. 8A, FIG. 8B, FIG. 9A, FIG. 9B, FIG. 10A, FIG.10B, FIG. 11A and FIG. 11B.

First, as illustrated in FIG. 6A and FIG. 6B, the n-type cladding layer321 made of an n-type AlGaAs layer, the active layer 322 made of a stackof AlGaAs layers and GaAs layers, the p-type first cladding layer 323made of a p-type AlGaAs layer, and the current blocking layer 324 madeof an n-type AlGaAs layer are successively grown on the n-type GaAssubstrate 300 by an MOCVD method or an MBE method.

Then, as illustrated in FIG. 7A and FIG. 7B, the current blocking layer324 is provided with a groove portion extending in the direction of theoptical waveguide by photolithography and etching so that the p-typefirst cladding layer 323 is exposed, after which the p-type secondcladding layer 325 made of a p-type AlGaAs layer and the contact layer326 made of a p-type GaAs layer are successively grown on the p-typefirst cladding layer 323 and the pair of current blocking layers 324 byan MOCVD method or an MBE method, thereby producing a first tentativesemiconductor laminated structure 340.

Then, as illustrated in FIG. 8A and FIG. 8B, a front-side portion of thefirst tentative semiconductor laminated structure 340 is removed byetching until the n-type GaAs substrate 300 is exposed, therebyproducing the second semiconductor laminated structure 320, which is therear-side portion of the first tentative semiconductor laminatedstructure 340.

Then, as illustrated in FIG. 9A and FIG. 9B, the n-side cladding layer311 having the same thickness as the-n-side cladding layer 321 and madeof an n-type AlGaInP layer, the active layer 312 made of a stack ofAlGaInP layers and GaInP layers, the p-type first cladding layer 313made of a p-type AlGaInP layer, and the current blocking layer 314 madeof an n-type AlInP layer are successively grown on the front-side regionof the n-type GaAs substrate 300 and the second semiconductor laminatedstructure 320 by an MOCVD method or an MBE method. Then, the currentblocking layer 314 is provided with a groove portion extending in thedirection of the optical waveguide so that the p-type first claddinglayer 313 is exposed, after which the p-type second cladding layer 315made of a p-type AlGaInP layer and the contact layer 316 made of ap-type GaAs layer are successively grown thereon again by an MOCVDmethod or an MBE method, thereby producing a second tentativesemiconductor laminated structure 350.

Then, as illustrated in FIG. 10A and FIG. 10B, a portion of the secondtentative semiconductor laminated structure 350 existing above thesecond semiconductor laminated structure 320 is removed by etching,thereby producing the first semiconductor laminated structure 310, whichis the front-side portion of the second tentative semiconductorlaminated structure 350. In this way, there remains the side-wall growthportion 338 made of a laminated structure including AlGaInP on the rearend portion of the first semiconductor laminated structure 310 which iscloser to the second semiconductor laminated structure 320. Theside-wall growth portion 338 is produced only to a very small thicknessdue to the difference between the orientation of the crystal growthsurface of the side-wall growth portion 338 and that of the frontsurface of the second semiconductor laminated structure 320.

Then, as illustrated in FIG. 11A and FIG. 11B, the groove portion 334extending in a direction perpendicular to the direction of the opticalwaveguide is provided along the junction between the contact layer 316of the first semiconductor laminated structure 310 and the contact layer326 of the second semiconductor laminated structure 320, after which thefirst p-type electrode 317 is provided on the contact layer 316 and thesecond p-type electrode 327 is provided on the contact layer 326. On thebottom surface of the n-type GaAs substrate.300, there is provided then-type electrode 333. Then, the front cleavage plane 331 of the firstsemiconductor laminated structure 310 is coated with the non-reflectioncoating layer 336 and the rear cleavage plane 332 of the secondsemiconductor laminated structure 320 is coated with the high-reflectioncoating layer 337.

According to the method for fabricating a semiconductor laser device ofEmbodiment 3, the semiconductor laser device is fabricated by growingthe first tentative semiconductor laminated structure 340 having thesame laminated structure as that of the second semiconductor laminatedstructure 320 on the n-type GaAs substrate 300, removing a front-sideportion of the first tentative semiconductor laminated structure 340,thereby forming the second semiconductor laminated structure 320 on therear-side region of the n-type GaAs substrate 300, growing the secondtentative semiconductor laminated structure 350 having the samelaminated structure as that of the first semiconductor laminatedstructure 310 on the front-side region of the n-type GaAs substrate 300and on the second semiconductor laminated structure 320, and removing aportion of the second tentative semiconductor laminated structure 350existing above the second semiconductor laminated structure 320, therebyproducing the first semiconductor laminated structure 310 on thefront-side region of the n-type GaAs substrate 300. Alternatively, thesemiconductor laser device may be fabricated by growing a firsttentative semiconductor laminated structure having the same laminatedstructure as that of the first semiconductor laminated structure 310 onthe n-type GaAs substrate 300, removing a rear-side portion of the firsttentative semiconductor laminated structure, thereby producing the firstsemiconductor laminated structure 310 on the front-side region of then-type GaAs substrate 300, growing a second tentative semiconductorlaminated structure having the same laminated structure as that of thesecond semiconductor laminated structure 320 on the rear-side region ofthe n-type GaAs substrate 300 and on the first semiconductor laminatedstructure 310, and removing a portion of the second tentativesemiconductor laminated structure existing above the first semiconductorlaminated structure 310, thereby producing the second semiconductorlaminated structure 320 on the rear-side region of the n-type GaAssubstrate 300.

FIRST VARIATION OF EMBODIMENT 3

A semiconductor laser device according to the first variation ofEmbodiment 3 of the present invention will now be described withreference to FIG. 12 and FIG. 13. FIG. 12 is a perspective, viewillustrating the semiconductor laser device according to the firstvariation of Embodiment 3, and FIG. 13 is a cross-sectional view takenalong XIII-XIII of FIG. 12.

In the first variation of Embodiment 3, the same elements as those ofEmbodiment 3 described above with reference to FIG. 4 and FIG. 5 will beprovided with the same reference numerals and will not be furtherdescribed below.

A feature of the first variation of Embodiment 3 is that the side-wallgrowth portion 338 does not protrude above the bottom surface of thegroove portion 334, and the upper surface of the side-wall growthportion 338 and the bottom surface of the groove portion 334 arecoplanar with each other, as illustrated in FIG. 12 and FIG. 13.

The portion of the side-wall growth portion 338 protruding above thebottom surface of the groove portion 334 is removed by etching in thestep of forming the groove portion 334 along the junction between thecontact layer 316 of the first semiconductor laminated structure 310 andthe contact layer 326 of the second semiconductor laminated structure320 (see FIG. 11A and FIG. 11B).

SECOND VARIATION OF EMBODIMENT 3

A semiconductor laser device according to the second variation ofEmbodiment 3 and a method for fabricating the same will now be describedwith reference to FIG. 14A and FIG. 14B. FIG. 14A is a perspective viewillustrating the semiconductor laser device according to the secondvariation of Embodiment 3, and FIG. 14B is a cross-sectional view takenalong line XIVb-XIVb of FIG. 14A.

In the second variation of Embodiment 3, the same elements as those ofEmbodiment 3 described above with reference to FIG. 4 and FIG. 5 will beprovided with the same reference numerals and will not be furtherdescribed below.

A feature of the second variation of Embodiment 3 is a groove portion334A provided along the junction between the first semiconductorlaminated structure 310 and the second semiconductor laminated structure320. The groove portion 334A extends in a direction perpendicular to thedirection of the optical waveguide and has a T-shaped cross section. Thegroove portion 334A is filled with a dielectric member 339 made of amaterial such as a refractive index matching resin, silicon oxide orsilicon nitride. Thus, the first semiconductor laminated structure 310and the second semiconductor laminated structure 320 are electricallyinsulated from each other.

Since the first semiconductor laminated structure 310 which oscillates ared laser beam has an oscillation threshold current which is greaterthan that of the second semiconductor laminated structure 320 whichoscillates an infrared laser beam, there is a possibility that areactive current, although in a slight amount, may flow from the firstsemiconductor laminated structure 310 to the second semiconductorlaminated structure 320 during operation of the first semiconductorlaminated structure 310. In the second variation, however, the reactivecurrent does not flow because the insulative dielectric member 339 isprovided along the junction between the first semiconductor laminatedstructure 310 and the second semiconductor laminated structure 320.

The refractive index of the dielectric member 339 preferably has a valuebetween the effective refractive index of the stripe region 312 a of theactive layer 312 of the first semiconductor laminated structure 310 andthat of the stripe region 322 a of the active layer 322 of the secondsemiconductor laminated structure 320.

In this way, the optical coupling efficiency between the first laserbeam emitted from the active layer 312 of the first semiconductorlaminated structure 310 and the active layer 322 of the secondsemiconductor laminated structure 320 is improved, and the opticalcoupling efficiency between the second laser beam emitted from theactive layer 322 of the second semiconductor laminated structure 320 andthe active layer 312 of the first semiconductor laminated structure 310is also improved, thereby improving the optical characteristics of thesemiconductor laser device.

The semiconductor laser device according to the second variation ofEmbodiment 3 can be fabricated as follows. After the groove portion 334is provided along the junction between the contact layer 316 of thefirst semiconductor laminated structure 310 and the contact layer 326 ofthe second semiconductor laminated structure 320 (see FIG. 13), theside-wall growth portion 338 is removed by etching so as to provide theT-shaped groove portion 334A, and then the T-shaped groove portion 334Ais filled with the dielectric member 339.

EMBODIMENT 4

A semiconductor laser device according to Embodiment 4 of the presentinvention will now be described with reference to FIG. 15A and FIG. 15B.FIG. 15A is a perspective view illustrating the semiconductor laserdevice according to Embodiment 4, and FIG. 15B is a cross-sectional viewtaken along line XVb-XVb of FIG. 15A.

As illustrated in FIG. 15A and FIG. 15B, a first semiconductor laminatedstructure 410 which includes an AlGaInP layer and has an oscillationwavelength in a 650 nm band is provided on a front-side region of ann-type GaAs substrate 400, and a second semiconductor laminatedstructure 420 which includes an AlGaAs layer and has an oscillationwavelength in a 780 nm band is provided on a rear-side region of then-type GaAs substrate 400.

The first semiconductor laminated structure 410 includes: an n-typecladding layer 411 made of an n-type AlGaInP layer; an active layer 412made of a stack of AlGaInP layers (barrier layers) and GaInP layers(well layers); a first p-type cladding layer 413 made of a p-typeAlGaInP layer; a pair of current blocking layers 414 made of an n-typeAlInP layer; a second p-type cladding layer 415-made of a p-type AlGaInPlayer; and a contact layer 416 made of a p-type GaAs layer. These layersare successively provided in this order on the front-side region (withrespect to the laser beam emitting direction) of the n-type GaAssubstrate 400. On the upper surface of the contact layer 416, there isprovided a first p-type electrode 417 which is in ohmic contact with thecontact layer 416. The composition of the mixed crystal of the activelayer 412 is selected so that the laser oscillation wavelength thereofis generally in a 650 nm band.

The second semiconductor laminated structure 420 includes: an n-typecladding layer 421 made of an n-type AlGaAs layer; an active layer 422made of a stack of AlGaAs layers (barrier layers) and GaAs layers (welllayers); a first p-type cladding layer 423 made of a p-type AlGaAslayer; a pair of current blocking layers 424 made of an n-type AlGaAslayer; a second p-type cladding layer 425 made of a p-type AlGaInPlayer;.and a contact layer 426 made of a p-type GaAs layer. These layersare successively provided in this order on the rear-side region (withrespect to the laser beam emitting direction) of the n-type GaAssubstrate 400. On the upper surface of the contact layer 426, a secondp-type electrode 427 which is in ohmic contact with the contact layer426 is provided with an interval from the first p-type electrode 417.The composition of the mixed crystal of the active layer 422 is selectedso that the laser oscillation wavelength thereof is generally in a 780nm band.

On the bottom surface of the n-type GaAs substrate 400, there isprovided an n-type electrode 433 which is in ohmic contact with thesubstrate 400.

A front cleavage plane 431 of the active layer 412 of the firstsemiconductor laminated structure 410 is coated with a non-reflectioncoating film 436 made of a dielectric film such as silicon oxide,silicon nitride or aluminum oxide. A rear cleavage plane 432 of then-type electrode 433 of the second semiconductor laminated structure 420is coated with a high-reflection coating film 437 including a dielectricfilm such as silicon oxide, silicon nitride or aluminum oxide, and anamorphous silicon film, or the like, which are laminated on each other.

The first feature of Embodiment 4 is that the thickness of the n-typecladding layer 411 of the first semiconductor laminated structure 410 isgreater than that of the n-type cladding layer 421 of the secondsemiconductor laminated structure 420. As a result, a stripe region 412a of the active layer 412 of the first semiconductor laminated,structure 410 is located above a stripe region 422 a of the active layer422 of the second semiconductor laminated structure 420.

More specifically, the thickness of the n-type cladding layer 411 of thefirst semiconductor laminated structure 410 is greater than the totalthickness of the n-type cladding layer 421, the active layer 422 and thefirst p-type cladding layer 423 of the second semiconductor laminatedstructure 420, and the total thickness of the n-type cladding layer 411,the active layer 412 and the first p-type cladding layer 413 of thefirst semiconductor laminated structure 410 is less than the totalthickness of the n-type cladding layer 421, the active layer 422, thefirst p-type cladding layer 423 and the second p-type cladding layer 425of the second semiconductor laminated structure 420. As a result, therear surface of the stripe region 412 a of the active layer 412 of thefirst semiconductor laminated structure 410 is attached to the frontsurface of the second p-type cladding layer 425 of the secondsemiconductor laminated structure 420.

The second feature of Embodiment 4 is that the composition of the secondp-type cladding layer 415 of the first semiconductor laminated structure410 and that of the second p-type cladding layer 425 of the secondsemiconductor laminated structure 420 are same.

The operation of the semiconductor laser device according to Embodiment4 of the present invention will now be described.

First, when a current is injected from the first p-type electrode 417,the injected current is confined into a region between the pair ofcurrent blocking layers 414 in the second p-type cladding layer 415,thereby oscillating a first laser beam having an oscillation wavelengthin a 650 nm band in the stripe region 412 a.

Since the composition of the second p-type cladding layer 415 of thefirst semiconductor laminated structure 410 and that of the secondp-type cladding layer 425 of the second semiconductor laminatedstructure 420 are same, there is no reflection of laser beam at aninterface 435 due to a difference in refractive index and absorptioncoefficient. Therefore, the first laser beam is oscillated with thefront cleavage plane 431 and the rear cleavage plane 432 servingsubstantially as resonator surfaces, and is emitted as a laser beamhaving a wavelength in a 650 nm band from the front cleavage plane 431which is coated with the non-reflection coating film 436.

Thus, since the energy gap of the second p-type cladding layer 425 ofthe second semiconductor laminated structure 420 is greater than that ofthe active layer 412 of the first semiconductor laminated structure 410,the second p-type cladding layer 425 is transparent to the first laserbeam, whereby no optical absorption loss occurs in the secondsemiconductor laminated structure 420.

While the composition of the second p-type cladding layer 415 of thefirst semiconductor laminated structure 410 and that of the secondp-type cladding layer 425 of the second semiconductor laminatedstructure 420 are same in Embodiment 4, the present invention is notlimited to this as long as the energy gap of the second p-type claddinglayer 425 is greater than that of the active layer 412 of the firstsemiconductor laminated structure 410.

When a current is injected from the second p-type electrode 427, theinjected current is confined into a region between the pair of currentblocking layers 424 in the second p-type cladding layer 425, therebyoscillating a second laser beam having an oscillation wavelength in a780 nm band in the stripe region 422 a.

The front surface of the stripe region 422 a of the active layer 422 ofthe second semiconductor laminated structure 420 is attached to the rearsurface of the n-type cladding layer 411 of the first semiconductorlaminated structure 410. Since the n-type cladding layer 411 made of ann-type AlGaInP layer is transparent to the second laser beam, the secondlaser beam is oscillated with the front cleavage plane 431 and the rearcleavage plane 432 serving as resonator surfaces. Moreover, since therear cleavage plane 432 is coated with the high-reflection coating film437, the second laser beam having a wavelength in a 780 nm band isemitted from the front cleavage plane 431.

Therefore, according to Embodiment 4, a region of the front cleavageplane 431 corresponding to the stripe region 412 a of the active layer412 serves as a light-emitting spot for the first laser beam, whileanother region of the front cleavage plane 431 below the stripe region412 a of the active layer 412 serves as a second light-emitting spot,thereby realizing a two-wavelength semiconductor laser device having twolight-emitting spots which are vertically arranged with each other andadjacent to each other. In such a case, the pitch between the firstlight-emitting spot and the second light-emitting spot is very small ascompared to that of a two-wavelength semiconductor laser device in whichthe first semiconductor laminated structure and the second semiconductorlaminated structure are horizontally arranged with each other.

In Embodiment 4, the active layer 412 of the first semiconductorlaminated structure 410 is located above the active layer 422 of thesecond semiconductor laminated structure 420 with respect to thesubstrate surface. Alternatively, the active layer 422 of the secondsemiconductor laminated structure 420 may be located above the activelayer 412 of the first semiconductor laminated structure 410. In such acase, the composition of a semiconductor layer in the secondsemiconductor laminated structure 420 which opposes the active layer 412of the first semiconductor laminated structure 410 can be madesubstantially the same as that of the n-type cladding layer 411 of thefirst semiconductor laminated structure 410.

In Embodiment 4, the first semiconductor laminated structure 410includes an AlGaInP layer and the second semiconductor laminatedstructure 420 includes an AlGaAs layer. Alternatively, it is possible toemploy the combination of a first semiconductor laminated structurelocated on the front side and including an AlGaN layer and a secondsemiconductor laminated structure located on the rear side and includingan AlGaInP layer so that a blue-violet laser beam in a 400 nm band and ared laser beam in a 650 nm band are emitted. Alternatively, it ispossible to employ the combination of a first semiconductor laminatedstructure located on the front side and including an AlGaN layer and asecond semiconductor laminated structure located on the rear side andincluding an AlGaAs layer so that a blue-violet laser beam in a 400 nmband and an infrared laser beam in a 780 nm band are emitted. In atwo-wavelength semiconductor laser device, the semiconductor laminatedstructure emitting a laser beam of the shorter wavelength is preferablyarranged on the laser beam emitting side.

A method for fabricating the semiconductor laser device according toEmbodiment 4 will now be described.

A first fabrication method is as follows. The first semiconductorlaminated structure 410 and the second semiconductor laminated structure420 in which the thickness of the n-type cladding layer 411 is greaterthan that of the n-type cladding layer 421 are produced separately.Then, the first semiconductor laminated structure 410 is fixed to afront-side region of the n-type GaAs substrate 400 by using a solder, orthe like, the second semiconductor laminated structure 420 is fixed to arear-side region of the n-type GaAs substrate 400 by using a solder, orthe like, and the first semiconductor laminated structure 410 and thesecond semiconductor laminated structure 420 are attached to each otheralong the interface 435. This is done so that the center line of thestripe region 412 a of the active layer 412 of the first semiconductorlaminated structure 410 and that of the stripe region 422 a of theactive layer 422 of the second semiconductor laminated structure 420 arealigned with each other. With the first fabrication method, sinceneither the first semiconductor laminated structure 410 nor the secondsemiconductor laminated structure 420 needs to be provided throughcrystal growth on the n-type GaAs substrate 400, a conductive substrate,e.g., a silicon substrate, may be used instead of the n-type GaAssubstrate 400.

A second fabrication method is as follows. The first semiconductorlaminated structure 410 is provided on the n-type GaAs substrate 400,with the second semiconductor laminated structure 420 being providedseparately. After a rear-side region of the first semiconductorlaminated structure 410 is removed by etching, the second semiconductorlaminated structure 420 is attached to the rear-side region.Alternatively, the second semiconductor laminated structure 420 isprovided on the n-type GaAs substrate 400, with the first semiconductorlaminated structure 410 being provided separately. After a front-sideregion of the second semiconductor laminated structure 420 is removed byetching, the first semiconductor laminated structure 410 is attached tothe front-side region. This is done so that the center line of thestripe region 412 a of the active layer 412 of the first semiconductorlaminated structure 410 and that of the stripe region 422 a of theactive layer 422 of the second semiconductor laminated structure 420 arealigned with each other.

EMBODIMENT 5

A semiconductor laser device according to Embodiment 5 of the presentinvention will now be described with reference to FIG. 16A and FIG. 16B.FIG. 16A is a perspective view illustrating the semiconductor laserdevice according to Embodiment 5, and FIG. 16B is a cross-sectional viewtaken along line XVIb-XVIb of FIG. 16A.

As illustrated in FIG. 16A and FIG. 16B, a first semiconductor laminatedstructure 510 which includes an AlGaInP layer and has an oscillationwavelength in a 650 nm band is provided on a front-side region (withrespect to the laser beam emitting direction) of a substrate 500 whichis made of, for example, a conductive silicon material, and a secondsemiconductor laminated structure 520 which includes an AlGaAs layer andhas an oscillation wavelength in a 780 nm band is provided on arear-side region (with respect to the laser beam emitting direction) ofthe substrate 500, with a gap 534 between the first semiconductorlaminated structure 510 and the second semiconductor laminated structure520.

The first semiconductor laminated structure 510 includes an active layer512 whose mixed crystal composition is selected so that the laseroscillation wavelength thereof is in a 650 nm band. The front surface ofthe first semiconductor laminated structure 510 is coated with anon-reflection coating film 536, and the rear surface of the firstsemiconductor laminated structure 510 is coated with a first surfacecoating film 538 whose reflectance is greater than that of thenon-reflection coating film 536.

The second semiconductor laminated structure 520 includes an activelayer 522 whose mixed crystal composition is selected so that the laseroscillation wavelength thereof is in a 780 nm band. The rear surface ofthe second semiconductor laminated structure 520 is coated with ahigh-reflection coating film 537, and the front surface of the secondsemiconductor laminated structure 520 is coated with a second surfacecoating film 539 whose reflectance is less than that of thehigh-reflection coating film 537.

In Embodiment 5, the center line between a pair of current blockinglayers in the first semiconductor laminated structure 510 and thatbetween a pair of current blocking layers in the second semiconductorlaminated structure 520 are aligned with each other, and the thicknessof an n-type cladding layer of the first semiconductor laminatedstructure 510 and that of an n-type cladding layer of the secondsemiconductor laminated structure 520 are set to be equal to each other.As a result, the center line of a stripe region of the active layer 512of the first semiconductor laminated structure 510 and that of a striperegion of the active layer 522 of the second semiconductor laminatedstructure 520 are aligned with each other.

The operation of the semiconductor laser device according to Embodiment5 will now be described.

First, when a current is injected into the first semiconductor laminatedstructure 510, a first laser beam having an oscillation wavelength in a650 nm band is oscillated in the active layer 512 of the firstsemiconductor laminated structure 510 with a portion of thenon-reflection coating film 536 and a portion of the first surfacecoating film 538 which correspond to the active layer 512 serving asresonator surfaces, and the first laser beam is emitted from thenon-reflection coating film 536.

When a current is injected into the second semiconductor laminatedstructure 520, a second laser beam having an oscillation wavelength in a780 nm band is oscillated in the active layer 522 of the secondsemiconductor laminated structure 520 with a portion of the secondsurface coating film 539 and a portion of the high-reflection coatingfilm 537 which correspond to the active layer 522 serving as resonatorsurfaces, and the second laser beam is emitted from-the second surfacecoating film 539.

Therefore, according to Embodiment 5, the second laser beam propagatesthrough a stripe-shaped optical waveguide which is made of the activelayer 512 of the first semiconductor laminated structure 510, and isemitted from a light-emitting spot in the non-reflection coating film536 which is defined by the optical waveguide of the first semiconductorlaminated structure 510. As a result, it is possible to realize atwo-wavelength semiconductor laser device which emits the first laserbeam and the second laser beam from a single light-emitting spot.

In Embodiment 5, the center line of the stripe region of the activelayer 512 of the first semiconductor laminated structure 510 and that ofthe stripe region of the active layer 522 of the second semiconductorlaminated structure 520 are aligned with each other. Alternatively, asin Embodiment 4, the center line of the stripe region of the activelayer 512 of the first semiconductor laminated structure 510 may belocated above or below that of the stripe region of the active layer 522of the second semiconductor laminated structure 520. Also in such acase, as long as the first semiconductor laminated structure 510 locatedon the front side is transparent to the second laser beam, two laserbeams having different wavelengths can be oscillated from twolight-emitting spots which are vertically arranged with each other andadjacent to each other.

In Embodiment 5, the first semiconductor laminated structure 510includes an AlGaInP layer and the second semiconductor laminatedstructure 520 includes an AlGaAs layer. Alternatively, it is possible toemploy the combination of a first semiconductor laminated structurelocated on the front side and including an AlGaN layer and a secondsemiconductor laminated structure located on the rear side and includingan AlGaInP layer so that a blue-violet laser beam in a 400 nm band and ared laser beam in a 650 nm band are emitted. Alternatively, it ispossible to employ the combination of a first semiconductor laminatedstructure located on the front side and including an AlGaN layer and asecond semiconductor laminated structure located on the rear side andincluding an AlGaAs layer so that a blue-violet laser beam in a 400 nmband and an infrared laser beam in a 780 nm band are emitted. In atwo-wavelength semiconductor laser device, the semiconductor laminatedstructure emitting a laser beam of the shorter wavelength is preferablyarranged on the laser beam emitting side.

A method for fabricating the semiconductor laser device according toEmbodiment 5 will now be described.

First, the first semiconductor laminated structure 510 in the form of achip (first laser chip) and the second semiconductor laminated structure520 in the form of a chip (second laser chip) are provided separately.The first semiconductor laminated structure 510 has the non-reflectioncoating film 536 on the front surface thereof and the first surfacecoating film 538 whose reflectance is greater than that of thenon-reflection coating film 536 on the rear surface thereof, and thesecond semiconductor laminated structure 520 has the high-reflectioncoating film 537 on the rear surface thereof and the second surfacecoating film 539 whose reflectance is less than that of thehigh-reflection coating film 537 on the front surface thereof.

Then, the first semiconductor laminated structure 510 is fixed to afront-side region of the substrate 500 by using a solder, or the like,and the second semiconductor laminated structure 520 is fixed to arear-side region of the substrate 500 by using a solder, or the like,with the gap 534 between the first semiconductor laminated structure 510and the second semiconductor laminated structure 520. This is done sothat the center line of the stripe region of the active layer 512 of thefirst semiconductor laminated structure 510 and that of the striperegion of the active layer 522 of the second semiconductor laminatedstructure 520 are aligned with each other.

VARIATION OF EMBODIMENT 5

A semiconductor laser device according to a variation of Embodiment 5will now be described with reference to FIG. 17. FIG. 17 is aperspective view illustrating the semiconductor laser device accordingto the variation of Embodiment 5.

In the variation of Embodiment 5, the same elements as those ofEmbodiment 5 described above with reference to FIG. 16A and FIG. 16Bwill be provided with the same reference numerals and will not befurther described below.

A feature of the variation of Embodiment 5 is, that the gap 534 betweenthe first semiconductor laminated structure 510 and the secondsemiconductor laminated structure 520 on the substrate 500 is filledwith a dielectric member 540 made of a material such as a refractiveindex matching resin, silicon oxide or silicon nitride, as illustratedin FIG. 17, and the refractive index of the dielectric member 540 has avalue between the effective refractive index of the stripe region of theactive layer 512 of the first semiconductor laminated structure 510 andthat of the stripe region of the active layer 522 of the secondsemiconductor laminated structure 520.

Therefore, the first semiconductor laminated structure 510 and thesecond semiconductor laminated structure 520 are electrically insulatedfrom each other by the dielectric member 540. Moreover, the opticalcoupling efficiency between the first laser beam emitted from the activelayer 512 of the first semiconductor laminated structure 510 and theactive layer 522 of the second semiconductor laminated structure 520 isimproved. Thus, the optical characteristics of the semiconductor laserdevice are improved.

EMBODIMENT 6

A semiconductor laser device according to Embodiment 6 of the presentinvention will now be described with reference to FIG. 18. FIG. 18 is across-sectional view illustrating the semiconductor laser deviceaccording to Embodiment 6.

As illustrated in FIG. 18, the semiconductor laser device according toEmbodiment 6 includes a first semiconductor laminated structure 610which includes an AlGaInN layer and has an oscillation wavelength in a400 nm band, a second semiconductor laminated structure 620 whichincludes an AlGaInP layer and has an oscillation wavelength in a 650 nmband, and a third semiconductor laminated structure 630 which includesan AlGaAs layer and has an oscillation wavelength in a 780 nm band.These semiconductor laminated structures are provided successively inthis order from the front side to the rear side (with respect to thelaser beam emitting direction) of a substrate 600 which is made of aconductive silicon material.

The first semiconductor laminated structure 610 includes an active layer612 whose mixed crystal composition is selected so that the laseroscillation wavelength thereof is in a 400 nm band, and the frontsurface of the first semiconductor laminated structure 610 is coatedwith a non-reflection coating film 636. The second semiconductorlaminated structure 620 includes an active layer 622 whose mixed crystalcomposition is selected so that the laser oscillation wavelength thereofis in a 650 nm band. The third semiconductor laminated structure 630includes an active layer 632 whose mixed crystal composition is selectedso that the laser oscillation wavelength thereof is in a 780 nm band,and the rear surface of the third semiconductor laminated structure 630is coated with a high-reflection coating film 637.

The gap between the first semiconductor laminated structure 610 and thesecond semiconductor laminated structure 620 on the substrate 600 isfilled with a first dielectric member 638 made of a material such as arefractive index matching resin, silicon oxide or silicon nitride. Therefractive index of the first dielectric member 638 has a value betweenthe effective refractive index of the stripe region of the active layer612 of the first semiconductor laminated structure 610 and that of thestripe region of the active layer 622 of the second semiconductorlaminated structure 620.

The gap between the second semiconductor laminated structure 620 and thethird semiconductor laminated structure 630 on the substrate 600 isfilled with a second dielectric member 639 made of a material such as arefractive index matching resin, silicon oxide or silicon nitride. Therefractive index of the second dielectric member 639 has a value betweenthe effective refractive index of the stripe region of the active layer622 of the second semiconductor laminated structure 620 and that of thestripe region of the active layer 632 of the third semiconductorlaminated structure 630.

The center line between a pair of current blocking layers in the firstsemiconductor laminated structure 610 and that between a pair of currentblocking layers in the second semiconductor laminated structure 620 arealigned with each other, and the thickness of an n-type cladding layerof the first semiconductor laminated structure 610 and that of an n-typecladding layer of the second semiconductor laminated structure 620 areset to be equal to each other. Moreover, the center line between thepair of current blocking layers in the second semiconductor laminatedstructure 620 and that between a pair of current blocking layers in thethird semiconductor laminated structure 630 are aligned with each other,and the thickness of the n-type cladding layer of the secondsemiconductor laminated structure 620 and that of an n-type claddinglayer of the third semiconductor laminated structure 630 are set to beequal to each other.

As a result, the center line of the stripe region of the active layer612 of the first semiconductor laminated structure 610, that of thestripe region of the active layer 622 of the second semiconductorlaminated structure 620, and that of the stripe region of the activelayer 632 of the third semiconductor laminated structure 630 are alignedwith one another.

The operation of the semiconductor laser device according to Embodiment6 will now be described.

First, when a current is injected into the first semiconductor laminatedstructure 610, a first laser beam having an oscillation wavelength in a400 nm band is oscillated in the stripe region of the active layer 612of the first semiconductor laminated structure 610. Since the secondsemiconductor laminated structure 620 has a large absorption coefficientfor the first laser beam having the oscillation wavelength in a 400 nmband, the first laser beam cannot easily propagate into the secondsemiconductor laminated structure 620. Thus, the first laser beam isoscillated with the non-reflection coating film 636 and the firstdielectric member 638 serving as resonator surfaces, and the first laserbeam is emitted from the non-reflection coating film 636.

When a current is injected into the second semiconductor laminatedstructure 620, a second laser beam having an oscillation wavelength in a650 nm band is oscillated in the stripe region of the active layer 622of the second semiconductor laminated structure 620. Since the firstsemiconductor laminated structure 610 has a small absorption coefficientfor the second laser beam having the oscillation wavelength in a 650 nmband and thus is transparent thereto, and the third semiconductorlaminated structure 630 has a large absorption coefficient for thesecond laser beam, the second laser beam cannot easily propagate intothe third semiconductor laminated structure 630. Thus, the second laserbeam is oscillated with the front surface of the first semiconductorlaminated structure 610 and the second semiconductor laminated structure620 serving as resonator surfaces, and the second laser beam is emittedfrom the non-reflection coating film 636.

When a current is injected into the third semiconductor laminatedstructure 630, a third laser beam having an oscillation wavelength in a780 nm band is oscillated in the active layer 632 of the thirdsemiconductor laminated structure 630. Since the first semiconductorlaminated structure 610 and the second semiconductor laminated structure620 both have a small absorption coefficient for the third laser beamhaving the oscillation wavelength in a 780 nm band and thus aretransparent thereto, the third laser beam is oscillated with thenon-reflection coating film 636 and the second dielectric member 639serving as resonator surfaces, and the third laser beam is emitted fromthe non-reflection coating film 636.

Therefore, according to Embodiment 6, the second laser beam propagatesthrough a stripe-shaped optical waveguide which is made of the activelayer 612 of the first semiconductor laminated structure 610, and isemitted from a light-emitting spot in the non-reflection coating film636. The third laser beam propagates through the stripe-shaped opticalwaveguide which is made of the active layer 612 of the firstsemiconductor laminated structure 610 and through a stripe-shapedoptical waveguide which is made of the active layer 622 of the secondsemiconductor laminated structure 620, and is emitted from alight-emitting spot in the non-reflection coating film 636. Thus, thesecond laser beam and the third laser beam are emitted from the samelight-emitting spot as the first laser beam, and it is possible torealize a three-wavelength semiconductor laser device which emits threelaser beams having different wavelengths from a single light-emittingspot.

In Embodiment 6, the center line of the stripe region of the activelayer 612 of the first semiconductor laminated structure 610, that ofthe stripe region of the active layer 622 of the second semiconductorlaminated structure 620, and that of the stripe region of the activelayer 632 of the third semiconductor laminated structure 630 are alignedwith one another. Alternatively, the center line of the stripe region ofthe active layer 612 of the first semiconductor laminated structure 610and that of the stripe region of the active layer 622 of the secondsemiconductor laminated structure 620 may be vertically offset from eachother, while the center line of the stripe region of the active layer632 of the third semiconductor laminated structure 630 is aligned withthat of the stripe region of the active layer 612 of the firstsemiconductor laminated structure 610 or that of the stripe region ofthe active layer 622 of the second semiconductor laminated structure620. In this way, it is possible to realize a three-wavelengthsemiconductor laser device which emits three laser beams havingdifferent wavelengths from two light-emitting spots which are verticallyarranged with each other.

A method for fabricating the semiconductor laser device according toEmbodiment 6 will now be described with reference to FIG. 18, FIG. 19Ato FIG. 19C, and FIG. 20.

First, the first semiconductor laminated structure 610 in the form of achip (first laser chip) whose front surface is coated with thenon-reflection coating film 636, the second semiconductor laminatedstructure 620 in the form of a chip -(second laser chip), and the thirdsemiconductor laminated structure 630 in the form of a chip (third laserchip) whose rear surface is coated with the high-reflection coating film637, as illustrated in FIG. 18, are produced by using an epitaxialgrowth method such as an MOVPE method and a minute processing methodsuch as a lithography method and an etching method.

Then, the first semiconductor laminated structure 610 is fixed to afront-side region of the substrate 600 by using a solder, or the like,as illustrated in FIG. 19A.

Then, the second semiconductor laminated structure 620 is fixed to arear-side region of the substrate 600 with respect to the firstsemiconductor laminated structure 610 (a central region of the substrate600) by using a solder, or the like, with a gap between the firstsemiconductor laminated structure 610 and the second semiconductorlaminated structure 620, as illustrated in FIG. 19B. This is done sothat the center line of the stripe region of the active layer 612 of thefirst semiconductor laminated structure 610 and that of the striperegion of the active layer 622 of the second semiconductor laminatedstructure 620 are aligned with each other.

Then, the third semiconductor laminated structure 630 is fixed to arear-side region of the substrate 600 with respect to the secondsemiconductor laminated structure 620 by using a solder, or the like,with a gap between the second semiconductor laminated structure 620 andthe third semiconductor laminated structure 630, as illustrated in FIG.19C. This is done so that the center line of the stripe region of theactive layer 622 of the second semiconductor laminated structure 620 andthat of the stripe region of the active layer 632 of the thirdsemiconductor laminated structure 630 are aligned with each other.

The order in which the first, second and third semiconductor laminatedstructures 610, 620 and 630 are fixed to the substrate 600 is notlimited to any particular order as long as the first semiconductorlaminated structure 610 is fixed to the front-side region of thesubstrate 600, the second semiconductor laminated structure 620 is fixedto the central region of the substrate 600 and the third semiconductorlaminated structure 630 is fixed to the rear-side region of thesubstrate 600.

Then, the gap between the first semiconductor laminated structure 610and the second semiconductor laminated structure 620 on the substrate600 is filled with the first dielectric member 638, and the gap betweenthe second semiconductor laminated structure 620 and the thirdsemiconductor laminated structure 630 on the substrate 600 is filledwith the second dielectric member 639, as illustrated in FIG. 20.

1. A method for fabricating a semiconductor laser device, thesemiconductor laser device comprising: a first semiconductor laminatedstructure which is provided on a front-side region of a substrate andincludes a first active layer for oscillating a first laser beam havinga first wavelength band; and a second semiconductor laminated structurewhich is provided on a rear-side region of the substrate and includes asecond active layer for oscillating a second laser beam having a secondwavelength band, the method comprising the steps of: growing a firsttentative semiconductor laminated structure having the same laminatedstructure as the second semiconductor laminated structure on thesubstrate; removing a front-side portion of the first tentativesemiconductor laminated structure, thereby producing the secondsemiconductor laminated structure on the rear-side region of thesubstrate; growing a second tentative semiconductor laminated structurehaving the same laminated structure as the first semiconductor laminatedstructure on the front-side region of the substrate and on the secondsemiconductor laminated structure; and removing a portion of the secondtentative semiconductor laminated structure above the secondsemiconductor laminated structure, thereby producing the firstsemiconductor laminated structure on the front-side region of thesubstrate.
 2. The method for fabricating a semiconductor laser device ofclaim 1, wherein an emission direction of the first laser beam and anemission direction of the second laser beam are collinear with eachother.
 3. The method for fabricating a semiconductor laser device ofclaim 1, wherein an emission direction of the second laser beam is aboveor below an emission direction of the first laser beam.
 4. The methodfor fabricating a semiconductor laser device of claim 1, wherein anenergy gap of the first active layer is greater than an energy gap ofthe second active layer.
 5. The method for fabricating a semiconductorlaser device of claim 1, wherein: the first active layer contains indiumand phosphorus; and the second active layer contains gallium andarsenic.
 6. The method for fabricating a semiconductor laser device ofclaim 1, further comprising the steps of: coating a front surface of thefirst semiconductor laminated structure with a non-reflection coatinglayer; and coating a rear surface of the second semiconductor laminatedstructure with a high-reflection coating layer.
 7. A method forfabricating a semiconductor laser device, the semiconductor laser devicecomprising: a first semiconductor laminated structure which is providedon a front-side region of a substrate and includes a first active layerfor oscillating a first laser beam having a first wavelength band; and aSecond semiconductor laminated structure which is provided on arear-side region of the substrate and includes a second active layer foroscillating a second laser beam having a second wavelength band, themethod comprising the steps of: growing a first tentative semiconductorlaminated structure having the same laminated structure as the firstsemiconductor laminated structure on the substrate; removing a rear-sideportion of the first tentative semiconductor laminated structure,thereby producing the first semiconductor laminated structure on thefront-side region of the substrate; growing a second tentativesemiconductor laminated structure having the same laminated structure asthe second semiconductor laminated structure on the rear-side region ofthe substrate and on the first semiconductor laminated structure; andremoving a portion of the second tentative semiconductor laminatedstructure above the first semiconductor laminated structure, therebyproducing the second semiconductor laminated structure on the rear-sideregion of the substrate.
 8. The method for fabricating a semiconductorlaser device of claim 7, wherein an emission direction of the firstlaser beam and an emission direction of the second laser beam arecollinear with each other.
 9. The method for fabricating a semiconductorlaser device of claim 7, wherein an emission direction of the secondlaser beam is above or below an emission direction of the first laserbeam.
 10. The method for fabricating a semiconductor laser device ofclaim 7, wherein an energy gap of the first active layer is greater thanan energy gap of the second active layer.
 11. The method for fabricatinga semiconductor laser device of claim 7, wherein: the first active layercontains indium and phosphorus; and the second active layer containsgallium and arsenic.
 12. The method for fabricating a semiconductorlaser device of claim 7, further comprising the steps of: coating afront surface of the first semiconductor laminated structure with anon-reflection coating layer; and coating a rear surface of the secondsemiconductor laminated structure with a high-reflection coating layer.13. A method for fabricating a semiconductor laser device, comprising: afirst step of providing a first laser chip including a first activelayer for oscillating a first laser beam having a first wavelength bandand a second laser chip including a second active layer for oscillatinga second laser beam having a second wavelength band; and a second stepof fixing the first laser chip to a front-side region of a substrate andfixing the second laser chip to a rear-side region of the substrate,wherein the second step comprises the step of fixing the first laserchip and the second laser chip so that an emission direction of thefirst laser beam and an emission direction of the second laser beam aresame.
 14. The method for fabricating a semiconductor laser device ofclaim 13, wherein the emission direction of the first laser beam and theemission direction of the second laser beam are collinear with eachother.
 15. The method for fabricating a semiconductor laser device ofclaim 13, wherein the emission direction of the second laser beam isabove or below the emission direction of the first laser beam.
 16. Themethod for fabricating a semiconductor laser device of claim 13, whereinan energy gap of the first active layer is greater than an energy gap ofthe second active layer.
 17. The method for fabricating a semiconductorlaser device of claim 13, wherein: the first active layer containsindium and phosphorus; and the second active layer contains gallium andarsenic.
 18. The method for fabricating a semiconductor laser device ofclaim 13, wherein after the second step, the method further comprisesthe step of filling a gap between a rear surface of the first laser chipand a front surface of the second laser chip with a dielectric memberhaving a refractive index which is between an effective refractive indexof a stripe region of the first active layer and an effective refractiveindex of a stripe region of the second active layer.
 19. A method forfabricating a semiconductor laser device, comprising: a first step ofproviding a first laser chip including a first active layer foroscillating a first laser beam having a first wavelength band, a secondlaser chip including a second active layer for oscillating a secondlaser beam having a second wavelength band, and a third laser chipincluding a third active layer for oscillating a third laser beam havinga third wavelength band; and a second step of fixing the first laserchip to a front-side region of a substrate, fixing the second laser chipto a central region of the substrate, and fixing the third laser chip toa rear-side region of the substrate, wherein the second step comprisesthe step of fixing the first laser chip, the second laser chip and thethird laser chip so that an emission direction of the first laser beam,an emission direction of the second laser beam, and an emissiondirection of the third laser beam are same.
 20. The method forfabricating a semiconductor laser device of claim 19, wherein theemission direction of the third laser beam is collinear with theemission direction of the first laser beam or the emission direction ofthe second laser beam.
 21. The method for fabricating a semiconductorlaser device of claim 19, wherein: an energy gap of the first activelayer is greater than an energy gap of the second active layer; and theenergy gap of the second active layer is greater than an energy gap ofthe third active layer.
 22. The method for fabricating a semiconductorlaser device of claim 19, wherein: the first active layer containsgallium and nitrogen; the second active layer contains indium andphosphorus; and the third active layer contains gallium and arsenic. 23.The method for fabricating a semiconductor laser device of claim 19,wherein after the second step, the method further comprises the stepsof: filling a gap between a rear surface of the first laser chip and afront surface of the second laser chip with a first dielectric memberhaving a refractive index which is between an effective refractive indexof a stripe region of the first active layer and an effective refractiveindex of a stripe region of the second active layer; and filling a gapbetween a rear surface of the second laser chip and a front surface ofthe third laser chip with a second dielectric member having a refractiveindex which is between the effective refractive index of the striperegion of the second active layer and an effective refractive index of astripe region of the third active layer.